1. Field of the Invention
The present invention relates generally to a method of fabricating rotary bits and components thereof for drilling subterranean formations. Particularly, the inventive method relates to manufacturing a "green" bit body or bit body component from particulate matter, machining the "green" bit body to define various structures and features, and binding the particles to one another. The method may be employed to fabricate an entire bit body, or bit body components which may be subsequently assembled with other components to form the bit body.
2. State of the Art
A typical rotary drill bit includes a bit body secured to a steel shank having a threaded pin connection for attaching the bit body to a drill string and a crown comprising that part of the bit fitted with cutting structures for cutting into an earth formation. Generally, if the bit is a fixed-cutter or so-called "drag" bit, the cutting structures include a series of cutting elements formed, at least in part, of a super abrasive material, such as natural diamond or polycrystalline diamond. The bit body is generally formed of steel or a matrix of hard particulate material such as tungsten carbide (WC) infiltrated with a binder, generally of copper alloy.
In the case of steel body bits, the bit body is typically machined from round stock to the desired shape, although cast bits are known in the art. Internal passages for delivery of drilling fluid to the bit face and topographical features defined at precise locations on the bit face may be machined into the bit body using a computer-controlled five-axis machine tool. Hardfacing for resisting abrasion during drilling is usually applied to the bit face and to other critical areas of the bit exterior, and cutting elements are secured to the bit face, generally by inserting the proximal ends of studs on which the cutting elements are mounted into apertures bored in the bit face. The end of the bit body opposite the face is then threaded, made up and welded to the bit shank.
In the case of a matrix-type bit body, it is conventional to employ a preformed, so-called bit "blank" of steel or other suitable material within the bit body matrix for attachment of the bit body to a hardened American Petroleum Institute (API) thread connection. The blank may be merely cylindrically tubular, or may be fairly complex in configuration and include protrusions corresponding to blades, wings or other features on and extending from the bit face. Other preform elements or displacements, comprised of cast resin-coated sand or, in some instances, tungsten carbide particles in a binder, may be employed to define internal passages for delivery of drilling fluid to the bit face, as well as cutting element sockets, ridges, lands, nozzle displacements, junk slots and other external topographic features of the bit. The blank and other displacements are placed at appropriate locations and orientations in the mold used to cast the bit body. The blank is bonded to the matrix upon cooling of the bit body after infiltration of the tungsten carbide particles with the binder in a furnace, and the other displacements are removed once the matrix has cooled. The upper end of the blank is then threaded, made up with a matingly hardened, threaded shank, and the two welded together. The cutting elements (typically diamond, and most often a synthetic polycrystalline diamond compact or PDC) may be bonded to the bit face during furnacing of the bit body if thermally stable PDC's, commonly termed TSP's (Thermally Stable Products), are employed, or may be subsequently bonded thereto, usually by brazing or mechanical affixation.
As may be readily appreciated from the foregoing description, the process of fabricating a matrix-type drill bit is a somewhat costly, complex multi-step process requiring separate fabrication of an intermediate product (the mold) before the end product (the bit) can be cast. Moreover, the blanks, molds, and any preforms employed must be individually designed and fabricated.
The mold used to cast a matrix body is typically machined from a cylindrical graphite element. For many years, bit molds were machined to a general bit profile, and the individual bit face topography defined in reverse in the mold by skilled technicians employing a profile mold and wielding dental-type drills and other fine sculpting tools. In more recent years, many details may be machined in a mold using a computer controlled five-axis machine tool. In some cases, the mold fabrication process has been made faster and less costly by use of rubber displacements duplicating in fine detail the topography of an entire bit profile and face, which displacements are then used to cast a ceramic bit mold of appropriate interior configuration, which is then used to contain the blank and matrix particles to cast a bit body.
While matrix-type bits may offer significant advantages over prior art steel body bits in terms of abrasion- and erosion-resistance, and while recent advances in matrix technology have markedly increased the toughness and ductility of matrix bodies, in many cases, the higher cost of a matrix-type bit and the longer time to fabricate same may result in the customer choosing a cheaper steel body bit with a faster delivery time. In either case, the customer must choose between a tough but less abrasion-resistant bit and a more expensive, highly abrasion- and erosion-resistant bit with reduced toughness.
One method that is not so time-consuming and costly as traditional matrix-type fabrication techniques is layered-manufacturing as disclosed in U.S. Pat. No. 5,433,280, assigned to the assignee of the present invention and incorporated herein for all purposes by this reference. The '280 patent discloses a method of fabricating a drill bit body or bit component in a series of sequentially superimposed layers or slices. As disclosed, a drill bit is designed as a three-dimensional "solid" model using a computer-aided design (CAD) program, which allows the designer to size, configure and place all internal and external features of the bit, such as (by way of example) internal fluid passages and bit blank voids, and external cutter receptacles, rakes and locations, as well as the height, thickness, profile and orientation of lands and ridges on the bit face and the orientation, depth and profile of waterways on the bit face and junk slots on the bit gage. The CAD program then provides an ".STL" file (i.e., a file which represents the surface of the bit body), which may later be transformed into a solid model and numerically "sliced" into a large number of thin, planar layers by known processes employing known computer programs.
After the mathematical slicing or layering is performed, a horizontal platen is provided on which a granular or particulate material such as a tungsten carbide coated with a laser-reactive bonding agent such as a polymer, a resin, and/or a low melting point metal such as Wood's metal or a lead alloy, or tungsten carbide intermixed with such a laser-reactive bonding agent is deposited in a thin, uniform layer. A finely focused laser, a focused light source such as from an incandescent or discharge type of lamp, or other energy beam, programmed to follow the configuration of the exposed section or layer of the bit body, is directed on the powder layer to melt the bonding agent and bond the metal particles together in the areas of the layer represented as solid portions of the bit in the model. Another layer of powder is then substantially uniformly deposited over the first, now-bonded layer, after which the metal particles of the second layer are bonded to each other and simultaneously to the first layer by the laser. The process continues until all layers or slices of the bit, as represented by the solid model, have been deposited and bonded, resulting in a mass of bonded-particulate material comprising a bit body which faithfully depicts the computer model in every dimensional respect. In areas of each layer which are not to form a part of the completed article, the laser or other energy beam does not traverse and bond the particles. Thus, a drill bit, or at least a bit body comprised of bonded-particulate material, may be fabricated directly from the CAD-generated solid model without the necessity of designing and fabricating molds and without the delicate, artistic hand labor currently required for bit details.
In a variation of the layered-manufacturing process, a tungsten carbide or other suitable powder or mix of powders (either metallic or nonmetallic) having the desired physical characteristics for a matrix may be uniformly premixed with a powdered binder, such as a metallic or nonmetallic (e.g., polymeric) binder powder, the premix deposited in layers and the binder powder at least partially fused by a laser to bond the tungsten carbide particles into a matrix and define the bit body shape. After the layered-manufacturing process is completed, since the binder is already in place, the bit body may be heated to effect complete in situ infiltration of the matrix. Alternatively, layers of binder powder and matrix powder may be alternately deposited. In either case, additional binder may be placed on top of the bit body to infiltrate and fill any voids in the binder-consolidated metal powder matrix.
In another variation of the layered-manufacturing process, a binder-coated matrix material (e.g., tungsten carbide) may be dispersed into a layer, and the binder coating melted with a laser sufficiently to cohere the particles of each layer and adjacent layers to one another. The bit body may then be heated to complete the in situ infiltration of the matrix. Additional binder may also be employed, as noted above.
In yet another variation of the layered-manufacturing process, a layer of particulate material is dispersed into a layer, and the particles in selected areas of the layer affixed to one another by a polymeric adhesive or non-polymeric binder (e.g., water-glass). Due to the selective deposition of binder over the layer of particulate material in order to define a desired solid structure, this type of layered-manufacturing is typically referred to as "3D-Printing".
The bit body may then be placed in a furnace where it may be preheated to substantially remove the bonding agent. In such instances, certain metal powders may be at least preliminarily sintered or fused, such sintering to be enhanced or completed, if necessary, in a later furnacing operation.
If a powdered metal coated with bonding agent or metal intermixed with a bonding agent is employed as the particulate material as mentioned above, the resulting bit body is a porous and permeable metal mass akin to a sponge or an open-celled foam which can be imbibed with suitable hardenable infiltrants, either metallic, non-metallic, or a combination thereof, to complete the bit body. If an infiltrant in liquid form at room temperature, such as certain polymers, is employed, the bit may be mass infiltrated via capillary action, gravity, and/or pressurized flow at room temperature, while if an infiltrant that is solid at room temperature is employed, the bit would be mass infiltrated by capillary action, gravity, and/or pressurized flow in a furnace, induction coil, or by other heating methods known in the art of fabricating matrix-type drill bits from loose tungsten carbide powders contained in a mold.
The infiltration process may include pouring a castable material, such as ceramic, plaster, graphite slurry or other similar materials known in the art and able to withstand the high temperatures typically encountered during the infiltration process, around the particulate-based bit body or assembly to provide solid structure support upon solidification of the castable material. Similarly, the bit body or assembly may be dipped one or more times into a castable material, such as a ceramic, plaster, or graphite slurry, to form a relatively rigid material around the bit body. In either case, it is preferable to preplug any orifices or openings leading to internal passageways in the bit body so that castable material that may otherwise be difficult to remove therefrom does not accumulate inside the bit body or assembly. Such plugs may be comprised of sand, graphite particles, clay or other suitable materials known in the art.
Alternatively, the particulate-based bit body or assembly may be placed in a refractory vessel with granular material packed around the particulate-based bit body up to its uppermost surface. This granular material substantially completely surrounds all surfaces of the bit body and may be vibrated to more densely pack the granular material. Because the granular material maintains its granular form during infiltration and is non-wettable by the infiltrant, the granular material effectively forms a "pliable" mold. That is, the granular material continues to provide structural support for the bit body during infiltration as dimensions of the bit body change, such as by shrinkage that may occur as a bonding agent employed to preliminarily hold the metallic particles of the bit body together vaporizes. The granular material may not substantially sinter, tack, or otherwise strengthen during the infiltration process so as to avoid complicating its removal from the bit body following infiltration, and thus continues to support the bit body substantially throughout infiltration without substantial change in its supporting physical characteristics.
A granular material that sinters, chemically reacts, or otherwise strengthens during the infiltration process may be used to provide a more rigid mold to support the bit body. Such a mold would be particularly beneficial for bit bodies that undergo little or no shrinkage.
In addition, it may be sufficient that a substantially rigid mold may be employed to provide support primarily during the first stages of infiltration, wherein the metallic particles of the layered bit body are imbibed with a sufficient amount of infiltrant and/or sufficiently sintered so that the bit body can structurally support itself.
Additionally, a mold material may be selected that conforms by shrinking and/or expanding along with any shrinkage and/or expansion of the bit body during the infiltration process to maintain a substantially impermeable, conforming support structure. Such a mold also helps prevent infiltrant material from flowing out of the bit body and pooling in gaps that may otherwise form between the bit body and the interior surface of the mold if the dimensions of the mold remain constant relative to the varying dimensions of the bit body during infiltration.
All of the materials used to form the support structure and/or fill any internal cavities in the bit body are formed from materials that are non-wettable by the infiltrant. That is, these materials do not absorb or otherwise chemically or mechanically bond to or react with the infiltrant utilized for infiltration. Rather, these materials form a barrier, because of their non-wettable quality, around the bit body such that the infiltrant stays contained within the bit body and does not bind the support structure to the bit body. In addition, such molds or support structures may be formed from materials that are substantially permeable to gases and vapors generated during the infiltration process, so as to preclude the formation or retention of gas or vapor voids in the bit body being infiltrated.
If a wettable material is used to form the support structure, the bit body may be coated with an infiltrant-resistive material, such as boron nitride water-glass or other suitable materials known in the art, prior to being placed within, or surrounded by, the support material. The boron nitride may be simply sprayed or painted onto various surfaces of the bit body, or the bit body may be dipped into a container of a boron nitride suspension to form a barrier through which the infiltrant cannot flow out of the bit body and imbibe the wettable support structure. Thus, the non-wettable and impermeable (by the infiltrant) resistive coating keeps the molten infiltrant contained within the layered bit body. In addition, such a coating may aid in forming a better surface finish for the bit body as it creates an intermediate shell to which the layered part and the infiltrant can conform during infiltration. Moreover, due to its liquid consistency, the coating fills small voids, vugs or intricately configured areas that may not be completely, intimately contacted by the surrounding support material. During the coating process, it is generally desirable to leave at least one surface uncoated so that the bit body has at least one non-resistive or wettable surface through which to imbibe additional infiltrant, even if infiltrant is already present in the preformed particulate-based bit body. Such a resistive coating may also be used in conjunction with variations of the infiltration process, whether the support material is wettable or non-wettable, to help form a better surface finish and help ensure that the infiltrant does not flow out of the particulate-based bit body and into the support structure, pool in any voids, gaps or vugs present between the bit body and the support structure, or form an unwanted skin of infiltrant on the outer surface of the bit body.
After the particulate-based bit body has been properly supported, the article of manufacture and any supporting materials and/or structures are placed within a traditional furnace, an induction coil furnace, or other heating apparatus known in the art along with an infiltrant and heated until the infiltrant melts and substantially fully permeates the article of manufacture through the free surface exposed to the infiltrant. The materials used to infiltrate the particulate-based bit body are typically copper-based alloys containing other elements such as nickel, as known in the art of fabrication of matrix-type drill bits.
U.S. Pat. No. 5,433,280 also discloses a tungsten carbide or other suitable powder or mix of powders (either metallic or non-metallic) having desired physical characteristics for a matrix substantially uniformly premixed with a powdered polymeric (or other nonmetallic) or metallic infiltrant powder, the premix deposited in layers and the infiltrant powder at least partially fused by a laser to bond the tungsten carbide particles into a matrix and define the bit body shape. After the layering and fusing process is completed, since the infiltrant is already in place, the bit body is heated in a furnace to effect complete in situ infiltration of the matrix. In another alternative to the foregoing procedure, layers of matrix powder alternating with layers of infiltrant powder are deposited. In either case, additional infiltrant may be added during infiltration to fill any infiltrant-deprived voids in the infiltrant-consolidated metal powder matrix. If an infiltrant-coated tungsten carbide or other suitable powder or mix of powders in a layered fashion is employed, a laser may be used to melt the infiltrant coating at least enough to cohere each layer, and the completed bit body placed in a furnace for an in situ infiltration of the bit body, with additional infiltrant being provided if necessary, as noted above.
A support structure may also be employed with a bit body comprised of metallic particles intermixed with particles of an infiltrant material. With such a particulate-based bit body, it may not be necessary to leave at least one surface exposed for additional infiltrant to be imbibed into the bit body. Such a particulate-based bit body, however, may require structural support as described above.
It is known, however, that during the layered-manufacturing of bit bodies of bonded particulate material, anisotropies may occur. For example, a bit body may have a generally oval- or elliptical-shaped transverse cross section rather than the generally circular transverse cross-section that is typically desired. Similarly, the size, shape, and alignment of various internal and external features of the bit may be undesirably altered during layered-manufacturing processes.
It is also known that layer-manufactured bit bodies typically include surfaces which have a "stepped" appearance, which may be somewhat undesirable in features of the bit body which have low dimensional tolerances. Moreover, due to the complexity of state-of-the-art bit bodies, layered-manufacturing of porous bit body matrices typically requires the fabrication of very thin layers of complex shapes. Thus, the accurate and precise manufacture of layers with low dimensional tolerances may be somewhat time consuming.
Therefore, it would be advantageous to provide a relatively simple method of manufacturing a bit, bit component, or other article of manufacture that reduces the time and cost of producing the article of manufacture by layered-manufacturing processes without sacrificing the orientation, alignment and detail of the various features of the article of manufacture. Moreover, it would be advantageous to provide a method that corrects anisotropies, "stepping", and other imperfections that may be generated during layered-manufacturing processes.